1. Field of the invention
This invention relates to an excavating and propelling machine for laying pipelines underground, and more particularly to an excavating and propelling machine for laying pipelines underground provided with a device for comparatively large crushing plum-pudding stones mixed in the excavated earth and sand so as to enable the whole excavated earth and sand to be transported successively and discharged.
2. Description of the prior art
Conventional excavating and propelling machines for laying pipelines underground are arranged to excavate the earth and sand in front of them by a pilot excavator device connected to the leading end of lengths of pipes to be laid underground and to advance the whole excavating and propelling machine by means of a pipe propelling machine located in a lanching pit behind it. During the period, the excavated earth and sand is changed in a slurry state by the water supplied by a water supply pump through a water supply pipeline installed in the buried pipeline into the pilot excavating machine, and then discharged by a sand pump etc. through a slurry pipeline installed also in the buried pipeline. The size of plum-pudding stones mixed in the slurry which can be discharged at that time is limited to a range of one-third to one half of the diameter of the muddy water discharge pipe which is a slurry passage and that of the discharge pipe connected to the sand pump.
Thus, the size of an excavated earth and sand intake port formed in the cutter head of the pilot excavator device must be determined taking into consideration the diameter of the discharge pipe. Therefore, the excavating and propelling machines of this kind are disadvantageous in that they cannot be used for grounds containing plum-pudding stones which are larger than the size of the earth and sand intake port.